The hull surface of a large vessel corrodes and has floating materials in the sea attached thereto. In order to re-coat the corroding hull surface or remove the attached floating materials, divers work manually in the sea. This manual work is also performed for determining normality or abnormality of the hull surface. However, it takes a lot of time to examine or repair the entire hull surface and risks are inherent all the time in that the works are performed under the sea.
Recently, various robots have been developed operable in the sea in order to examine abnormality of the hull surface or repair the abnormality of the hull surface. In particular, robots are emerged which precisely examine and repair the hull surface while being attached to and moving on the hull surface. A location of an underwater robot, which works while being attached to the bottom surface of the hull, may be found in various ways. As a representative way of finding the location of the underwater robot, there is a long baseline (LBL), short baseline (SBL), or ultra short baseline (USBL) positioning system using an ultrasonic system.
In these ways, the location of the underwater operating robot may be calculated by installing on the bottom of the hull a plurality of acoustic transceivers which transmit ultrasonic waves, detecting ultrasonic waves which are reflected in response to the transmitted ultrasonic waves, and integrating a location relationship with each of the plurality of acoustic transceivers. However, these ways take a lot of time due to various devices installed in the sea.
Another way to calculate a location of an underwater robot working on the bottom portion of the hull is to compare terrain features by using a vision system or an ultrasonic scanner. However, it is also difficult to find a precise location in this way because singularity extraction is not easy when the hull surface is clean.
Therefore, an apparatus is necessary for finding a location of an underwater robot working while being attached to the bottom portion of the hull.